The hydraulic differential functions to vary the ratio between an input speed and an output speed. One example of such use of a hydraulic differential in a hydraulic transmission is disclosed in the Cordner et al. U.S. Pat. No. 4,252,035, owned by the assignee of this application.
The hydraulic differential has a pair of axial piston displacement units assembled together with a valve plate and a port plate positioned therebetween for directing flow between the two displacement units. One of the displacement units is of fixed displacement, as provided by a fixed angle wobbler associated with the pistons of the unit. The other displacement unit is of variable displacement and has a wobbler associated therewith which may be positioned at a selected angle to provide the desired ratio between the input and output speeds of the hydraulic differential.
Other examples of hydraulic differentials are disclosed in the Creighton et al. U.S. Pat. No. 3,131,539, and another patent owned by the assignee of this application, namely, Sugden U.S. Pat. No. 4,046,029.
The foregoing prior art does not disclose a relatively compact hydraulic differential utilizing floating port and valve plates between a pair of axial piston displacement units with a hydrostatic bearings between relatively movable components with yieldable loading of the port plate, as by a block spring of a displacement unit, and with the structure related to provide a closed force loop whereby relatively small radial bearings can be used for rotatable mounting of the components, with the bearings only required to react the block spring loading.